1. Field of the Invention
This invention relates to a stator core which can be used in a stator in an automobile alternator, for example, and a method of manufacture therefor.
2. Description of the Related Art
FIG. 7 is a perspective view showing a stator core used in the stator of a conventional automobile alternator.
This stator core 1 is composed of a single strip 2 made of sheet steel formed with tooth portions 2a and core back portions 2b, wound spirally such that the tooth portions 2a stack up in line with each other and the core back portions 2b stack up in line with each other, and the core 1 is arc welded on its outer surface so that the spirally wound strip is integrated. Furthermore, the welded portions 3 are disposed circumferentially at a prescribed pitch and further across the entire area in the direction of lamination on the outer surface of the wound strip 2.
Next, the conventional method of manufacture for a stator core 1 will be explained with reference to FIGS. 8 and 9.
First, 1 mm thick, 22 mm wide sheet steel 4 is fed to a press (not shown), which forms the single band of sheet steel 4 into two strips 2 having tooth portions 2a and core back portions 2b as shown in FIG. 8. Next, the two strips 2 are separated and each strip is fed to a winding device. As shown in FIG. 9, each strip 2 is wound around an internal diameter guide cylinder 5 from its leading end and moves downwards as the winding proceeds so that it forms a lamination. At this time, the wound strip 2 is formed to an internal diameter corresponding to the external diameter of the internal diameter guide cylinder 5. Also, the external diameter of the wound strip 2 is controlled by an external diameter guide cylinder 6.
The strip 2 is wound spirally under the control of the internal diameter guide cylinder 5 and the external diameter guide cylinder 6 until the lamination reaches a certain height (thickness) and is then cut. The wound strip 2 is then removed and its outer surface is arc welded to obtain a stator core 1.
As described above, the conventional method of manufacture for a stator core aims to cut costs by making use of the protrusions and recesses in the tooth portions 2a, punching two strips 2 with intermeshed protrusions and recesses from a single long band of sheet steel 4, so that two stator cores 1 can be manufactured from sheet steel 4 having the length necessary for one stator core 1.
However, the problem with the conventional method of manufacture is that the stator core 1 is manufactured by winding a single strip 2, and so if the height of the stator core 1 is increased to raise output, or the sheet is made thinner to reduce core loss, the time required to wind the strip 2 increases and production costs increase.